We form the past perfect progressive (sometimes called the "past perfect continuous") with had been + main verb + ing. We use this tense to talk about an on-going process that happened in the past before something else in the past.

For example, we might say, "She had been waiting for two hours when the bus finally arrived." The bus arrived in the past, and before that, she had been in the on-going process of waiting for it to come.

Past Perfect Progressive Grammar Quiz

I minding my own business when the canvasser stopped me on the street to talk about legalizing pot.

I had whether to call him for the last two days until he phoned and asked me out today.

been waiting very long before I met you?

Joy Division been attracting many fans until the lead singer killed himself and they became New Order.